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Disease Profile

Chromosome 18p duplication

Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.

<1 / 1 000 000

US Estimated

Europe Estimated

Age of onset






Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease.


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype.


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder.


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.


Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable


Other names (AKA)

Duplication 18p; Trisomy 18p; 18p duplication;


Congenital and Genetic Diseases


Chromosome 18p duplication is a rare chromosome abnormality in which there are three copies of the short (p) arm of chromosome 18 in each cell, rather than the usual two copies. The severity of the condition and the signs and symptoms depend on the size and location of the duplicated genetic material and which genes are involved.[1][2] A complete duplication of the p arm of chromosome 18 is rare.[3] Reported features include: intellectual disability, foot or hand anomalies, distinctive facial features, and epilepsy.[1][2][3][4] Chromosome 18p duplication may occur sporadically in a family with no previous history or may be inherited from a parent with the same duplication or another chromosome abnormality, such as a balanced translocation.[4] Treatment is based on the signs and symptoms present in each person.[1][2][3]


The severity of chromosome 18p duplication and the signs and symptoms present depend on the size and location of the duplicated genetic material and which genes are involved. Features commonly include: intellectual disability that ranges from mild to severe, characteristic facial features, and epilepsy. Other findings reported in the medical literature include: hand and foot anomalies, decreased muscle tone (hypotonia), and developmental delay.[1][2][5][3][4]

Some researchers have suggested that several of the cases reported in the medical literature may represent cases in which other chromosome changes are present but are not yet identified. This may help explain the variability in the signs and symptoms present.[2][5] It is additionally suspected that some individuals with chromosome 18p duplication may not be diagnosed if they have mild or absent signs and symptoms and are of normal intelligence.[2]

This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

Medical Terms Other Names
Learn More:
80%-99% of people have these symptoms
Abnormality of the pinna
Abnormally shaped ears
Auricular malformation
Deformed ears
Malformed ears

[ more ]

Attention deficit hyperactivity disorder
Attention deficit
Attention deficit disorder
Attention deficit-hyperactivity disorder
Attention deficits
Childhood attention deficit/hyperactivity disorder

[ more ]

Bilateral cryptorchidism
Narrow opening between the eyelids
Highly arched eyebrow
Arched eyebrows
Broad, arched eyebrows
High, rounded eyebrows
High-arched eyebrows
Thick, flared eyebrows

[ more ]

Abnormally close eyes
Closely spaced eyes

[ more ]

Intellectual disability, mild
Mental retardation, borderline-mild
Mild and nonprogressive mental retardation
Mild mental retardation

[ more ]

Midface retrusion
Decreased size of midface
Midface deficiency
Underdevelopment of midface

[ more ]

Voracious appetite
Preauricular skin tag
Pyloric stenosis
Sloping forehead
Inclined forehead
Receding forehead

[ more ]

Corners of eye widely separated
Thin vermilion border
Decreased volume of lip
Thin lips

[ more ]

Underdeveloped nasal alae
Underdeveloped tissue around nostril
Upslanted palpebral fissure
Upward slanting of the opening between the eyelids
Wide nasal bridge
Broad nasal bridge
Broad nasal root
Broadened nasal bridge
Increased breadth of bridge of nose
Increased breadth of nasal bridge
Increased width of bridge of nose
Increased width of nasal bridge
Nasal bridge broad
Wide bridge of nose
Widened nasal bridge

[ more ]

30%-79% of people have these symptoms
Abnormal foot morphology
Abnormal feet structure
Abnormality of the feet
Abnormality of the foot
Foot deformities
Foot deformity

[ more ]

Abnormality of finger
Abnormalities of the fingers
Narrow mouth
Small mouth
5%-29% of people have these symptoms
Abnormality of cardiovascular system morphology
Facial palsy
Bell's palsy
High, narrow palate
Narrow, high-arched roof of mouth
Narrow, highly arched roof of mouth

[ more ]

Intrauterine growth retardation
Prenatal growth deficiency
Prenatal growth retardation

[ more ]

Abnormally small skull
Decreased circumference of cranium
Decreased size of skull
Reduced head circumference
Small head circumference

[ more ]

Little lower jaw
Small jaw
Small lower jaw

[ more ]

Neonatal hypotonia
Low muscle tone, in neonatal onset
Short stature
Decreased body height
Small stature

[ more ]



Because the presence and severity of signs and symptoms vary from person to person, treatment also varies. If an intellectual disability and/or developmental delay is present, early educational intervention and early services are important.

It is essential to work with one's person's health care provider and medical team to determine the appropriate medical management plan.


Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

Organizations Supporting this Disease

    Learn more

    These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

    Where to Start

    • The National Human Genome Research Institute, part of the National Institutes of Health (NIH), has developed a fact sheet on chromosome abnormalities, which may be helpful to you. To read this information, visit the link.

      MedlinePlus, the National Library of Medicine Web site designed to direct you to information and resources that help you research your health questions, provides further information about chromosomes. Click on the link.

    • Genetics Home Reference (GHR) contains information on Chromosome 18p duplication. This website is maintained by the National Library of Medicine.

      In-Depth Information

      • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
      • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
      • PubMed is a searchable database of medical literature and lists journal articles that discuss Chromosome 18p duplication. Click on the link to view a sample search on this topic.


        1. Rodríguez L, Liehr T, Mrasek K, Mansilla E, Martínez-Fernández ML, Garcia A, Martínez-Frías ML. Small Supernumerary Chromosome Marker Generating Complete and Pure Trisomy 18p, Characterized by Molecular Cytogenetic Techniques and Review. American Journal of Medical Genetics Part A. 2007; 143A(22):2727-2732. https://www.ncbi.nlm.nih.gov/pubmed/17937429.
        2. Mabboux P, Brisset S, Aboura A, Pineau D, Kourbi V, Joannidis S et al. Pure and Complete Trisomy 18p Due to a Supernumerary Marker Chromosome Associated with Moderate Mental Retardation. American Journal of Medical Genetics Part A. 2007; 143A(7):727-733. https://www.ncbi.nlm.nih.gov/pubmed/17330860.
        3. Azoospermia and trisomy 18p syndrome: a fortuitous association? A patient report and a review of the literature. Guillaume Jedraszak, Henri Copin, Manuel Demailly, Catherine Quibel, Thierry Leclerc, Marlène Gallet, Moncef Benkhalifa, Aline Receveur. Molecular cytogenetics. June 4. 2015; 8(34):https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4453045/.
        4. Orendi K, Uhrig S, Mach M, Tschepper P, Speicher MR. Complete and pure trisomy 18p due to a complex chromosomal rearrangement in a male adult with mild intellectual disability.. American Journal of Medical Genetics (Part A). May 21, 2013; 161A(7):1806-1812. https://www.ncbi.nlm.nih.gov/pubmed/23695988.
        5. Schinzel A. Catalogue of Unbalanced Chromosome Aberrations in Man. New York: Walter de Gruyter; 2001;

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